You can prefer a surprise without making someone guess the entire definition of care.

Wanting to be surprised is a fair preference, and it can quietly become a test. If nobody is allowed to know what you like, what would please you or when you need help, then every attempt is a guess and every wrong guess reads as not knowing you at all. The spontaneity you enjoy still needs raw material. Telling people something about your tastes does not remove the surprise, it just narrows the field.

Give one clear piece of information about what you like this week. Let the other person decide the when and the how.